Many welding applications such as MIG (metal inert gas) or GMAW (gas metal arc welding) utilize a wire feeder to provide filler metal to the weld. Generally, the wire feeder will provide wire at a nominally constant speed (typically given in inches per minute). Wire feed speed controllers control the speed at which the wire is fed to the arc.
A typical prior art wire feeder includes a motor that pulls wire from a reel and feeds the wire to the weld arc. The motor is controlled by a wire feed controller that may be a stand alone controller or maybe part of a controller that controls other aspects of the welding process. The wire feed controller controls the speed of the wire feeder and typically includes a potentiometer on a front panel of the controller which the user uses to set wire feed speed.
A user selectable input, such as the angular position of a knob, typically determines the resistance of the potentiometer, which is used to set the speed point in the control circuit. The controller may include feedback circuitry to control the wire feed speed, or the speed control may be open loop.
The operator control panel label typically includes markings for the knob that indicate a percent of the maximum wire feed speed. The user selects the desired percentage of maximum wire feed speed. For example, at 100 percent, the wire feeder will operate at top speed, and at 50 percent the wire feeder will operate at one-half of its top speed. Wire feeder and welding machine user's manuals often include tables that indicate the percent setting on the potentiometer (knob) for various gauge (thickness) materials to be welded. Generally, lesser gauge material requires the wire be fed at a slower speed. A typical range for wire feed speeds is from 50 inches per minute for thinner material to 650 inches per minute for thicker material.
These,controls are simple and easy to implement. However, they have a significant drawback. Specifically, the potentiometer is substantially linear: the relationship between changes in angular position and changes in wire feed speed is linear over the entire range. For example, if the entire,range of wire feed speed is 600 inches per minute, and the total angular rotation 300 angular degrees, then two percent of the angular range (6 angular degrees) will result in 12 inches per minute difference in wire feed speed.
The sensitivity (inches/minute/degree of angular rotation) is determined by the relationship between angular position and wire feed speed. Thus, the precision by which wire feed speeds may be operatively selected is the same at the fast and slow end of the wire feed speed range.
However, when welding, the speed selection at the faster end of wire feed speed range (heavier gauge material) need not be as precise as the speed selection at the slower end of the wire feed speed range. For example, when operating at 600 inches per minute, being off by 5 or 10 inches per minute may not be significant. However, when operating at 50 inches per minute, being off by 5 or 10 inches per minute may be very significant and can confuse the operator since 175 inches/minute is available on both toggle switch positions. Thus, it is desirable that the control be more precise at slower wire feed speeds than at faster wire feed speeds.
Some prior art wire feed controllers overcame this drawback by providing a toggle switch to select between a faster range and a slower range. Thus, the angular sensitivity at slower speeds is greater than when using the potentiometer for the full range. However, this requires an additional control switch. Also, this prevented the use of a direct wire feed speed reading, since a single potentiometer knob was used for multiple wire feed speed ranges.
FIG. 1 is part of a panel of such a prior art wire feed control having a two-range speed control. Two control knobs are shown on this portion of the panel. Control knob 101 controls the wire feed speeds, and control knob 103 controls the output voltage (and is not particularly relevant to the present invention). Control knob 101 is part of a potentiometer which has an output provided to a controller.
A switch 102 selects between the fast and slow range of wire feed speeds. Specifically, when switch 102 is toggled to the left, the slow range (between 50 and 350 inches per minute) is selected. When switch 102 is toggled to the right, the full range (50 to 650 inches per minute) is selected. Thus, to select 175 inches per minute the user would toggle switch 102 to the left and select 50 percent on knob 101. This would provide 50 percent of the maximum (350) or 175 inches per minute. Should the user desire a wire feed speed of about 490 inches per minute switch 102 would be toggled to the right and the setting for knob 101 would be about 75 percent. This would provide approximately 490 inches per minute. However, this sort of design does not allow the wire feed speed to be displayed in inches per minute on the selector knob. Additionally, this does not allow the user to effectively access all wire feed speeds over the entire range, without toggling a switch.
Experienced welders will often know the wire feed speed necessary for the weld they are performing. Also, inexperienced welders can easily determine the necessary wire feed speed using a table or slide rule calculator. However, given the prior art wire feed speed control (which required the panel to show percent of maximum wire feed speed) even an experienced welder needed to consult the user's manual.
Another prior art wire feed controller is part of the Miller.TM. RCSP-45 (Remote Control Synergic Pulser) used for pulse MIG arc welding. This controller is complex and expensive and has two adjustment knobs: arc power and arc length. Neither knob directly controlled wire feed speed, although wire feed speed was determined based on the arc length and arc power selected. As used herein, a parameter is directly controlled when a selectable input--such as a knob on the operator panel--is used to control the parameter directly, rather than indirectly by altering other output parameters. The indirect control effected a non-linear change in wire feed speed for changes in arc length and arc power. However, this prior art did not allow independent control of the wire feed speed by a single knob.
Accordingly, it would be desirable to provide a wire feeder that provided an independent control of wire feed speed which was non-linear over the range of wire feed speeds. Additionally, the control should be such that the user may read the control in inches per minute, rather than percent of maximum speed.